WIP Feat: Add neighboring point search modes

Add an enum to configure how the vtkPCANormalEstimation filter selects the surrounding neighboring points used to calculate the PCA.

• To maintain the previous behavior, by default, N points are selected regardless of their location relative to the sampled point.
• A new approach simply selects neighboring points inside a radius, only the neighborhood of the sampled is considered. Give better results to estimate normals among groups of isolated points.